CVE-2026-28138: uListing Object Injection Vulnerability

CVE-2026-28138 Overview

A Deserialization of Untrusted Data vulnerability has been identified in the Stylemix uListing WordPress plugin that allows PHP Object Injection attacks. This vulnerability affects the uListing plugin through version 2.2.0 and enables authenticated attackers with high privileges to inject arbitrary PHP objects into the application.

Critical Impact

Authenticated attackers with administrative privileges can exploit this PHP Object Injection vulnerability to execute arbitrary code, manipulate application data, or escalate their access within the WordPress installation. The presence of suitable gadget chains in the application could lead to complete server compromise.

Affected Products

• Stylemix uListing WordPress Plugin versions up to and including 2.2.0
• WordPress installations running vulnerable versions of uListing

Discovery Timeline

• 2026-02-26 - CVE-2026-28138 published to NVD
• 2026-02-26 - Last updated in NVD database

Technical Details for CVE-2026-28138

Vulnerability Analysis

The vulnerability stems from insecure deserialization practices within the uListing WordPress plugin. When the plugin processes serialized PHP data from user-controlled input without proper validation, it creates an opportunity for attackers to inject malicious PHP objects. This is classified under CWE-502 (Deserialization of Untrusted Data).

PHP Object Injection vulnerabilities are particularly dangerous in WordPress environments because the extensive plugin ecosystem often includes "magic methods" (such as __wakeup(), __destruct(), or __toString()) that can be chained together to achieve code execution. An attacker who can control the serialized data passed to unserialize() can instantiate arbitrary objects and trigger these magic methods with attacker-controlled properties.

The attack requires authentication with high privileges (such as administrator or editor roles), which limits the immediate attack surface but still poses significant risk in scenarios involving compromised admin accounts or insider threats.

Root Cause

The root cause of this vulnerability is the use of PHP's unserialize() function on untrusted input without adequate validation or sanitization. The uListing plugin fails to implement proper input filtering or use safer alternatives like json_decode() for data serialization, allowing an attacker to craft malicious serialized payloads that instantiate dangerous objects upon deserialization.

Attack Vector

This vulnerability is exploitable over the network by an authenticated attacker with high-level privileges. The attacker would craft a specially formatted serialized PHP object payload and submit it through a vulnerable input vector within the uListing plugin interface. Upon deserialization, the malicious object is instantiated, potentially triggering a chain of method calls (Property-Oriented Programming or POP chains) that could result in:

• Remote code execution
• File read/write operations
• Database manipulation
• Privilege escalation within WordPress

The exploitation does not require user interaction and has the potential to impact confidentiality, integrity, and availability of the affected system. For detailed technical analysis, refer to the Patchstack Vulnerability Report.

Detection Methods for CVE-2026-28138

Indicators of Compromise

• Anomalous serialized PHP object strings containing unexpected class names in HTTP request parameters or POST data
• Unusual file system activity or new files created in WordPress directories following plugin interactions
• Unexpected database modifications associated with uListing plugin tables
• Error logs showing deserialization warnings or object instantiation failures

Detection Strategies

• Deploy Web Application Firewalls (WAF) with rules to detect serialized PHP object patterns in incoming requests
• Implement logging and monitoring for all administrative actions within the uListing plugin
• Use file integrity monitoring to detect unauthorized changes to WordPress core files and plugin directories
• Monitor for unusual outbound network connections from the WordPress server

Monitoring Recommendations

• Enable verbose PHP error logging to capture deserialization-related exceptions
• Configure security plugins to alert on suspicious administrative activity patterns
• Implement real-time log analysis for HTTP requests containing serialized data signatures
• Review access logs for repeated requests to uListing plugin endpoints from unusual sources

How to Mitigate CVE-2026-28138

Immediate Actions Required

• Update the Stylemix uListing plugin to a patched version beyond 2.2.0 when available
• Review and audit administrator accounts for any signs of compromise
• Implement additional access controls and multi-factor authentication for WordPress admin accounts
• Consider temporarily disabling the uListing plugin if a patch is not yet available and functionality is not critical

Patch Information

Organizations should monitor the Patchstack Vulnerability Report for official patch availability from Stylemix. Until a patch is released, implement the workarounds listed below to reduce exposure.

Workarounds

• Restrict access to the WordPress admin panel to trusted IP addresses only using .htaccess or server-level firewall rules
• Implement Web Application Firewall rules to block requests containing serialized PHP object patterns
• Reduce the number of administrator accounts and enforce strong password policies
• Use WordPress security plugins to add an additional layer of protection against object injection attacks

# Example: Restrict WordPress admin access by IP in .htaccess
<Files wp-login.php>
    Order Deny,Allow
    Deny from all
    Allow from 192.168.1.100
    Allow from 10.0.0.0/24
</Files>